Cells and cell theory

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课程笔记

What are cells?

Cells are the smallest structural and functional units of all living organisms.
All living things, including plants, animals, bacteria, and fungi, are made up of cells.
Cells are microscopic – they can only be seen with a microscope.
Robert Hooke first observed and named cells in 1665 using a microscope on cork.
Cells can differ in shape and size; different shapes usually mean they do different jobs.

Robert Hooke's microscope and his observation of cork cells.

Cell Theory

Cell theory states that all organisms are composed of cells.
Cells are alive and are the basic living units of organization in all organisms.
All cells come from other cells (Rudolf Virchow, 1858).
Many experiments support cell theory, and no evidence contradicts it.

Eukaryotic vs Prokaryotic Cells

The main difference is the presence of a nucleus: eukaryotic cells have a nucleus, prokaryotic cells do not.
Eukaryotic cells include plant and animal cells; prokaryotic cells include bacteria.
In prokaryotes, DNA floats in the cytoplasm without a membrane.
Eukaryotic cells have membrane-bound organelles, while prokaryotes generally do not.

Diagram of a prokaryotic cell with labeled parts.

Common Cell Structures

All cells have a cell membrane, cytoplasm, and (in most eukaryotes) a nucleus.
The cell membrane is a thin layer that encloses the cell and separates it from its environment.
The cell membrane is selectively permeable – it controls what enters and leaves the cell.
Cytoplasm includes all living parts of the cell within the membrane, excluding the nucleus.
Cytoplasm consists of cytosol (watery, jelly-like medium) and organelles.

Diagram of a cell with common structures labeled

Nucleus and DNA

The nucleus controls all processes and chemical reactions in the cell.
It contains the cell's genetic material organized into DNA molecules.
The nucleus is enclosed by a nuclear membrane with pores.
DNA contains information about inherited characteristics (hereditary traits).
Differences in DNA between individuals are called variation.

Diagram and micrograph of a cell nucleus.

Mitochondria

Mitochondria are organelles enclosed by a double membrane.
They are the site of cellular respiration, where food molecules are combined with oxygen to release energy.
Carbon dioxide, water, and waste are by-products of respiration.
Active cells (e.g., muscle cells) have more mitochondria than less active cells.
Mitochondria have their own DNA, different from nuclear DNA.

A micrograph of muscle tissue in a mouse showing mitochondria.

Specialized Cells

In multicellular organisms, cells are specialized to perform specific functions.
Red blood cells have a biconcave shape to trap oxygen and have a large surface area for oxygen transfer.
Nerve cells are long and stringy to form communication lines and send signals quickly.
Skin cells are flat and fit tightly together to protect the body.
A cell's function is partly based on its structure.

Red blood cells, neurons, and epidermal (skin) cells.

Unicellular vs Multicellular Organisms

Unicellular organisms (e.g., bacteria) consist of one cell that performs all life functions.
Multicellular organisms are made of many cells, often trillions, that work together.
Unicellular cells must perform metabolism, homeostasis, and reproduction on their own.
Multicellular cells may collaborate with other cells to perform functions.
Examples of multicellular organisms include protists (some), fungi, plants, and animals.

Unicellular and multicellular organisms under the microscope.

Plant vs Animal Cells

Plant and animal cells are similar but have key differences.
Plant cells have vacuoles that are often large and central; animal cells have smaller vacuoles.
Plant cells have chloroplasts for photosynthesis; animal cells do not.
Plant cells have a cell wall outside the cell membrane; animal cells do not.
Both have a nucleus, cytoplasm, cell membrane, and mitochondria.

A micrograph of a plant cell.

Levels of Organization

In multicellular organisms, specialized cells group together to form tissues.
Tissues work together to form organs.
Organs work together in organ systems.
Example: smooth muscle tissue contracts and enables movement; nerve cells send messages; red blood cells carry oxygen.

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练习题

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1.What is the smallest structural and functional unit of an organism?
Easy
- ACell
- BTissue
- COrgan
- DOrganism
2.Which scientist first observed cells in 1665 using a basic light microscope?
Easy
- ARobert Hooke
- BRudolf Virchow
- CAntonie van Leeuwenhoek
- DCharles Darwin
3.Which of the following is a key component of the cell theory?
Easy
- AAll cells come from non-living matter.
- BAll organisms are composed of cells.
- CCells can arise spontaneously.
- DOnly multicellular organisms are made of cells.
4.The cell membrane is selectively permeable, meaning it controls which substances enter and leave the cell.
Easy
True or false?
5.Which structure in a cell contains the genetic material (DNA) and controls the cell's processes?
Easy
- AMitochondrion
- BNucleus
- CVacuole
- DCytoplasm
6.Which of the following are components common to all cells? (Select all that apply)
Easy
- ACell membrane
- BNucleus
- CCytoplasm
- DMitochondria
- EChloroplasts
7.Arrange the following in order from smallest to largest level of organization in a multicellular organism.
Easy
- Cell
- Tissue
- Organ
- Organ system
8.Which type of cell would likely have more mitochondria?
Medium
- AMuscle cell
- BSkin cell
- CBone cell
- DRed blood cell

复习笔记

## Cells and Cell Theory - **Cell theory** (mid-1800s): 1. All living organisms are made of cells. 2. Cells are the basic structural/organizational unit of all organisms. 3. All cells come from pre-existing cells. - Cells are the basic unit of structure and reproduction in all living things. - Some organisms are **single-celled** (e.g., bacteria), others are **multicellular** (e.g., humans). - **Robert Hooke** (1665) first observed cells in cork using a compound microscope; he named them "cells" (Latin *cella* = small room). - **Anton van Leeuwenhoek** improved microscopes (up to 270× magnification) and observed living cells. - **Matthias Schleiden** and **Theodor Schwann** later confirmed cells in both plants and animals. - Modern microscopes include **optical** (light) and **electron** microscopes, allowing us to see tiny cell structures. - Note: Some biologists debate whether viruses (non-cellular) are alive, but cell theory applies to all cellular life.

Cell theory: A scientific theory stating that all living organisms are made of cells, cells are the basic unit of structure and organization, and all cells come from pre-existing cells.
Cell: The basic structural and functional unit of all living organisms; can be single-celled or part of a multicellular organism.
Robert Hooke: English scientist who first observed and named 'cells' in 1665 using a compound microscope.
Anton van Leeuwenhoek: Dutch scientist who improved microscopes and was the first to observe living cells.
Matthias Schleiden: German botanist who concluded that all plants are made of cells.
Theodor Schwann: German zoologist who concluded that all animals are made of cells.
Microscope: An instrument that uses lenses to magnify small objects, enabling the study of cells.

闪卡

What is the cell theory?

Cell theory states that all living organisms are made of cells, cells are the basic unit of structure and function in living things, and all cells come from pre-existing cells.

Who is credited with discovering cells?

Robert Hooke is credited with discovering cells in 1665 when he observed thin slices of cork under a microscope and saw tiny pores he called 'cells'.

What did Robert Hooke actually see when he observed cork cells?

Hooke saw the empty cell walls of plant tissues, not living cells with internal components.

Why did Hooke not think cells were alive?

Because his microscope had low magnification, he could not see internal components like the nucleus or organelles, so he thought the 'cellulae' were empty rooms.

What is the meaning of the Latin word 'cella'?

'Cella' means 'a small room', like monks lived in.

Who improved microscope lenses and achieved 270x magnification?

Anton van Leeuwenhoek made a single-lens microscope with a small glass sphere that achieved 270x magnification.

What was the maximum magnification before Leeuwenhoek's improvements?

Before Leeuwenhoek, the maximum magnification was about 50x.

What invention made it possible to view objects smaller than the wavelength of visible light?

The electron microscope, developed in the 1920s, made it possible to view objects smaller than optical wavelengths.

What did Matthias Schleiden and Theodor Schwann contribute to cell theory?

They studied both plant and animal cells and concluded that cells are fundamental to both plants and animals, supporting the idea that cells are the basic unit of life.

What is the basic structural and organizational unit of all organisms?

The cell is the basic structural and organizational unit of all organisms.

Are viruses considered living organisms under cell theory?

Some biologists consider viruses living, but cell theory traditionally applies only to cellular life; viruses are not made of cells.

What is the name of the book in which Hooke described his cell observations?

Micrographia.

What did Hooke mistakenly suggest about the origin of mold?

Hooke suggested spontaneous generation, the idea that life arises from non-living matter, because he could not see seeds or spores.

What is a compound microscope?

A compound microscope uses an objective lens and an eyepiece to achieve higher magnification than a simple microscope.

When did compound microscopes first appear in Europe?

Around 1620.

Who manufactured microscopes and hired Otto Schott and Ernst Abbe to improve lenses?

Carl Zeiss, a German engineer.

What limitation do optical microscopes have?

Optical microscopes can only focus on objects the size of a wavelength of light or larger.

What is the difference between a single-celled and a multicellular organism?

A single-celled organism consists of one cell that carries out all life functions, while a multicellular organism is made of many cells that work together.

What does MS-LS1-1 standard cover?

MS-LS1-1 covers evidence that living things are made of cells, and that cells are the basic unit of life.

What did Hooke use to illuminate specimens in his microscope?

He used reflected light for some observations and directly transmitted light for others.

What is the significance of the cell theory in biology?

Cell theory is the fundamental principle that all life is composed of cells, which are the basic units of structure, function, and reproduction.

Why did Hooke name the pores 'cells'?

He named them 'cells' because they reminded him of the small rooms (cellulae) in a monastery or the six-sided cells of a honeycomb.

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